Parallel link mechanism and industrial robot

ABSTRACT

A link mechanism arranged between a fixed base and a movable base. The mechanism includes a drive gear reducer, a first arm, a second arm, a connection base, a first link, and a second link. The drive gear reducer includes a body, an input shaft, a first output shaft, and a second output shaft. The first arm is connected to the fixed base and the body of the reducer. The second arm is connected to the second output shaft and the movable base. The connection base is arranged such that the second arm is between the connection base and the reducer, the connection base is connected to the first output shaft. The first link is connected to the fixed base and the connection base. The second link is connected to the connection base and the movable base.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. Ser. No.11/581,741 filed Oct. 16, 2006 based upon and claims the benefit ofpriority from prior Japanese Patent Application No. 2005-303416, filedon Oct. 18, 2005 and Japanese Patent Application No. 2006-167510, filedon Jun. 16, 2006, the entire contents of which are incorporated hereinby reference.

BACKGROUND

1. Technical Field

The present invention relates to a parallel link mechanism and anindustrial robot.

2. Related Art

General requirements for industrial robots include increased operationspeed, improved operation accuracy, and, in certain operation sites,enhanced cleanliness. There are demands that the industrial robots beused under particular circumstance involving use of specific gases orchemicals. One known vertical movement shaft mechanism of a SCARA robotincludes a ball screw provided in a vertical movement shaft. Themechanism has a contractible and extensible bellows as a protectingmember for preventing release of dust and leakage of grease from theinterior of an arm to the external environment.

However, when the bellows extends and contracts, the pressure in thevertical movement shaft mechanism changes, inducing the dust release andthe grease leakage. It is thus difficult for the vertical movement shaftmechanism having the bellows to maintain the increased cleanliness.Further, to sufficiently prolong mechanical life of the bellows of thevertical movement shaft mechanism, the bellows must be formed ofmaterial selected from a limited range. This makes it difficult tooperate the vertical shaft mechanism having the bellows under theaforementioned particular circumstances.

To solve the problem, a vertical movement shaft mechanism of anindustrial robot including a parallel link mechanism, but not a bellows,has been proposed. Specifically, as described in Japanese Laid-OpenPatent Publication No. 2002-326181, the mechanism includes a first armconnected to a fixed base and a connection base and a second armconnected to the connection base and a movable base. A drive motor isprovided in the fixed base and a plurality of spur gears are arranged inthe connection base. The drive motor drives the spur gears through areducer, causing the spur gears to transmit rotational force to the twoarms. This vertically moves the movable base.

The vertical movement shaft mechanism of Japanese Laid-Open PatentPublication No. 2002-326181 operates without using a bellows, or is abellows-less type. Instead, the mechanism includes a transmissionmechanism employing the spur gears for rotating the two arms. It is thusnecessary to engage the teeth of the spur gears together when assemblingthe industrial robot, which makes such assembly complicated.

SUMMARY

Accordingly, it is an objective of the present invention to provide aparallel link mechanism having a transmission mechanism easy to installand an industrial robot.

According to an aspect of the invention, a parallel link mechanismarranged between a fixed base and a movable base includes a harmonicdrive gear reducer, a first arm, a second arm, a connection base, afirst auxiliary link, and a second auxiliary link. The harmonic drivegear reducer has a body, an input shaft, a first output shaft, and asecond output shaft. The first arm has a proximal end pivotallyconnected to the fixed base and a distal end connected to the body ofthe reducer. The second arm has a proximal end connected to the secondoutput shaft and a distal end pivotally connected to the movable base.The connection base is arranged outside the second arm with respect tothe reducer and connected to the first output shaft. The first auxiliarylink is arranged parallel with the first arm and has an end pivotallyconnected to the fixed base and an end pivotally connected to theconnection base. The second auxiliary link is arranged parallel with thesecond arm and has an end pivotally connected to the connection base andan end pivotally connected to the movable base.

According to a second aspect of the invention, a parallel link mechanismarranged between a fixed base and a movable base includes a harmonicdrive gear reducer, a first arm, a second arm, a connection base, afirst auxiliary link, and a second auxiliary link. The harmonic drivegear reducer has a body, an input shaft, a first output shaft, and asecond output shaft. The first arm has a proximal end pivotallyconnected to the fixed base and a distal end connected to the secondoutput shaft. The second arm has a proximal end connected to the body ofthe reducer and a distal end pivotally connected to the movable base.The connection base is arranged outside the first arm with respect tothe reducer and connected to the first output shaft. The first auxiliarylink is arranged parallel with the first arm and has an end pivotallyconnected to the fixed base and an end pivotally connected to theconnection base. The second auxiliary link is arranged parallel with thesecond arm and has an end pivotally connected to the connection base andan end pivotally connected to the movable base.

According to a third aspect of the invention, an industrial robotincludes a first parallel link mechanism, a second parallel linkmechanism, and a harmonic drive gear mechanism. The first parallel linkmechanism has a fixed base, a connection base, a first arm, and a firstauxiliary link. The first arm has a proximal end pivotally connected tothe fixed base. The first auxiliary link is arranged parallel with thefirst arm. The first auxiliary link has an end pivotally connected thefixed base and an end pivotally connected to the connection base. Thesecond parallel link mechanism has the connection base, a movable base,a second arm, and a second auxiliary link. The second arm has a distalend pivotally connected to the movable base. The second auxiliary linkis arranged parallel with the second arm. The second auxiliary link hasan end pivotally connected to the connection base and an end pivotallyconnected to the movable base. The harmonic drive gear mechanism isarranged between the distal end of the first arm and the proximal end ofthe second arm. The harmonic drive gear mechanism includes a body, aninput shaft, a first output shaft, and a second output shaft. The bodyis connected to the distal end of the first arm. The input shaft isconnected to the drive motor. The first output shaft converts rotationof the input shaft and transmits the rotation to the connection base.The second output shaft converts rotation of the input shaft andtransmits the rotation to the second arm.

According to a fourth aspect of the invention, an industrial robotincludes a first parallel link mechanism, a second parallel linkmechanism, and a harmonic drive gear mechanism. The first parallel linkmechanism has a fixed base, a connection base, a first arm, and a firstauxiliary link. The first arm has a proximal end pivotally connected tothe fixed base. The first auxiliary link is arranged parallel with thefirst arm. The first auxiliary link has an end pivotally connected thefixed base and an end pivotally connected to the connection base. Thesecond parallel link mechanism has the connection base, a movable base,a second arm, and a second auxiliary link. The second arm has a distalend pivotally connected to the movable base. The second auxiliary linkis arranged parallel with the second arm. The second auxiliary link hasan end pivotally connected to the connection base and an end pivotallyconnected to the movable base. The harmonic drive gear mechanism isarranged between the distal end of the first arm and the proximal end ofthe second arm. The harmonic drive gear mechanism includes a body, aninput shaft, a first output shaft, and a second output shaft. The bodyis connected to the proximal end of the second arm. The input shaft isconnected to a drive motor. The first output shaft converts rotation ofthe input shaft and transmits the rotation to the connection base. Thesecond output shaft converts rotation of the input shaft and transmitsthe rotation to the first arm.

Other aspects and advantages of the invention will become apparent fromthe following description, taken in conjunction with the accompanyingdrawings, illustrating by way of example the principles of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention, together with objects and advantages thereof, may best beunderstood by reference to the following description of the presentlypreferred embodiments together with the accompanying drawings in which:

FIG. 1 is a side view showing an industrial robot according to anembodiment of the present invention;

FIG. 2 is a cross-sectional view showing the industrial robot of FIG. 1;

FIG. 3 is an enlarged cross-sectional view showing a drive motorincluding a harmonic drive gear reducer;

FIG. 4 is a diagram representing operation of the industrial robot ofFIG. 1; and

FIG. 5 is an enlarged cross-sectional view showing another example ofthe drive motor of FIG. 3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of the present invention will now be described withreference to FIGS. 1 to 4. FIG. 1 is a side view showing an industrialrobot 1. FIG. 2 is a cross-sectional view showing the industrial robot1.

As shown in FIG. 1, the industrial robot 1 has a substantiallyparallelepiped fixed base 2 fixed to a floor surface B. Referring toFIG. 2, the fixed base 2 has a cylindrical first connection shaft 5. Thefirst connection shaft 5 is rotatably supported by the fixed base 2through a bearing 4. The proximal portion of a first arm 3 is connectedto the first connection shaft 5. Specifically, a through hole 3H isdefined in the proximal portion of the first arm 3 and extends throughthe first arm 3, allowing communication between the interior and theexterior of the first arm 3. The first connection shaft 5 is secured tothe wall of the through hole 3H through securing bolts B1. This permitsthe first arm 3 to rotate about the axis L1 of the first connectionshaft 5. The connecting portion between the first connection shaft 5 andthe first arm 3 is sealed by an O ring (not shown). The first arm 3 hasa first arm cover 3 a, which defines a sealed space in the interior ofthe first arm 3.

A drive motor 10 is provided at the distal end of the first arm 3.

As shown in FIG. 3, the drive motor 10 includes a drive motor body 10 aand the harmonic drive gear reducer 10 b. The reducer 10 b has a body,or a body cover K, fixed to the distal end of the first arm 3 throughconnection bolts B2. The drive motor body 10 a is secured to the reducer10 b through a motor flange 13 by securing bolts B3. The drive motorbody 10 a has a cylindrical motor shaft 15. The motor shaft 15 projectstoward the reducer 10 b and is connected to an input shaft 21 of thereducer 10 b. The motor shaft 15 is firmly connected to the input shaft21 through, for example, a flange coupling in such a manner as toprevent the motor shaft 15 from becoming unstable with respect to theinput shaft 21 in a rotational direction. The drive motor body 10 afurther includes a motor housing 16 secured to the motor flange 13through the securing bolts B3. A sleeve 17 is secured to the motorhousing 16. The sleeve 17 rotatably supports the motor shaft 15 and theinput shaft 21 from inside the motor shaft 15 and the input shaft 21.The sleeve 17 defines a hollow space in the drive motor 10.

Rotational force generated by the motor shaft 15 is transmitted to theinput shaft 21. The input shaft 21 has a wave generator 22. The wavegenerator 22 has a cam portion 22 a having an oval cross-section, afirst ball bearing 22 b, and a second ball bearing 22 c. The cam portion22 a is secured to the input shaft 21. The first and second ballbearings 22 b, 22 c are arranged around the outer circumference of thecam portion 22 a. When the input shaft 21 rotates about the axis L2, theinner rings of the first and second ball bearings 22 b, 22 c rotateabout the axis L2 integrally with the cam portion 22 a.

A first flexspline 24 is formed around the outer ring of the first ballbearing 22 b. The first flexspline 24 has a substantially cup-likeshape. The first flexspline 24 has a cylindrical portion formed of anelastic metal body. The inner wall of the cylindrical portion is held incontact with the outer ring of the first ball bearing 22 b. When theinput shaft 21 (the cam portion 22 a) rotates, a cross-section of thecylindrical portion of the first flexspline elastically deforms in anoval shape along the outer peripheral surface of the cam portion 22 a.

Teeth (not shown) are formed on the outer circumference of thecylindrical portion of the first flexspline 24. A first output shaft 27is secured to a proximal portion 24 a of the first flexspline 24 througha non-illustrated connection bolt. The first output shaft 27 isrotatably supported by the input shaft 21 and rotates about the axis L2.

A second flexspline 25 is formed around the outer ring of the secondball bearing 22 c. The second flexspline 25 has a cylindrical portionformed of an elastic metal body and a flange portion 25 a extendingradially outward from an axial end of the cylindrical portion. The innerwall of the cylindrical portion is held in contact with the outer ringof the second ball bearing 22 c. When the input shaft 21 (the camportion 22 a) rotates about the axis L2, a cross-section of thecylindrical portion of the second flexspline 25 elastically deforms inan oval shape along the outer peripheral surface of the cam portion 22a. Teeth (not shown) are formed on the outer peripheral surface of thecylindrical portion of the second flexspline 25. The flange 25 a issecured to the cover K through securing bolts B4.

A cylindrical circular spline 26 is arranged around the first and secondflexsplines 24, 25. A second output shaft 29 is connected to an outerside of the circular spline 26 through a non-illustrated connectionbolt. The second output shaft 29 is rotatably supported by the firstoutput shaft 27 through a bearing arranged at an outer side of the firstoutput shaft 27. When the circular spline rotates, the second outputshaft 29 rotates about the axis L2.

A first gear portion 26 a and a second gear portion 26 b are formed atthe inner circumference of the circular spline 26 and engaged with thefirst flexspline 24 and the second flexspline 25, respectively. Thefirst gear portion 26 a has a greater number of teeth than the firstflexspline 24. The first gear portion 26 a becomes engaged with thefirst flexspline 24 solely in a direction defined by the longitudinalaxis, of the oval cam portion 22 a. The second gear portion 26 b has agreater number of teeth than the second flexspline 25. The second gearportion 26 b becomes engaged with the second flexspline 25 solely in adirection defined by the longitudinal axis of the cam portion 22 a.

In a single cycle of clockwise rotation of the input shaft 21, each ofthe teeth of the first gear portion 26 a relatively rotates the engagedone of the teeth of the first flexspline 24 in a counterclockwisedirection by an amount corresponding to the difference between thenumber of the teeth of the first gear portion 26 a and the number of thefirst flexspline 24. In other words, when the input shaft 21 rotates,the circular spline 26 rotates the first output shaft 27 relative to thefirst flexspline 24 in the direction opposite to the rotationaldirection of the input shaft 21. The circular spline 26 rotates thefirst output shaft 27 in accordance with the reduction ratiocorresponding to the difference between the number of the teeth of thefirst gear portion 26 a and the number of the teeth of the firstflexspline 24.

In a single cycle of clockwise rotation of the input shaft 21, each ofthe teeth of the second gear portion 26 b relatively rotates the engagedone of the teeth of the second flexspline 25 in a counterclockwisedirection by the amount corresponding to the difference between thenumber of the teeth of the second gear portion 26 b and the number ofthe teeth of the second flexspline 25. In other words, when the inputshaft 21 rotates, the circular spline 26 rotates the second output shaft29 relative to the second flexspline (the first arm 3) in the directionopposite to the rotational direction of the input shaft 21. The circularspline 26 rotates the second output shaft 29 in accordance with thereduction ratio corresponding to the difference between the number ofthe teeth of the second gear portion 26 b and the number of the teeth ofthe second flexspline 25.

That is, the first output shaft 27 receives rotation of the input shaft21 that has been converted into rotation in the opposite direction andreduced by the first flexspline 24 and the first gear portion 26 a ofthe circular spline 26. Similarly, the second output shaft 29 receivesrotation of the input shaft 21 that has been converted into rotation inthe opposite direction and reduced by the second flexspline 25 and thesecond gear portion 26 b of the circular spline 26.

The ratio of the reduction ratio of the first output shaft 27 to theinput shaft 21 to the reduction ratio of the second output shaft 29 tothe input shaft 21 can be varied by changing the number of the teeth ofeach of the first and second flexsplines 24, 25 and the first and secondgear portions 26 a, 26 b. In the illustrated embodiment, the number ofthe teeth of each of these components is selected so that the ratio ofthe reduction ratio of the first output shaft 27 to the input shaft 21and the reduction ratio of the second output shaft 29 to the input shaft21 become 2:1. In other words, the second output shaft 29 of theillustrated embodiment rotates in the same direction as that of thefirst output shaft 27 at a rotational angle twice as large as that ofthe first output shaft 27.

The lower end of the second arm 30 is connected to the second outputshaft 29. Specifically, a cylindrical portion 30 b formed in the lowerend of the second arm 30 is secured to the second output shaft 29through connection bolts B5 in such a manner that the cylindricalportion encompasses the outer circumference of the second output shaft29. Referring to FIG. 2, a movable base 40 having a substantiallybox-like shape is connected to the upper end of the second arm 30. Themovable base 40 has a cylindrical second connection shaft 43 rotatablysupported by a bearing 42. The upper end of the second arm 30 is securedto the second connection shaft 43 through securing bolts B6. The secondarm 30 is rotatably connected to the movable base 40 and rotates aboutthe axis L3 of the second connection shaft 43. The second arm 30 and thesecond connection shaft 43 are both hollow. The second arm 30 is sealedby a second arm cover 30 a and the connecting portion between the secondconnection shaft 43 and the second arm 30 is sealed by an O-ring (notshown).

As shown in FIG. 3, a connection base 50 is arranged outside the secondarm 30 with respect to the reducer 10 b (at the left-hand side as viewedin FIG. 2) and secured to the first output shaft 27. The connection basehas a cup-like connecting portion 51 and an extended portion 52 securedto the connecting portion 51. The connecting portion 51 is fixed to thefirst output shaft 27 through connection bolts B7. The connectingportion 51 has a connecting portion cover 51 a and a seal member 57. Theconnecting portion cover 51 a and the seal member 57 seal the spacebetween the connection base 50 and the second arm 30 in such a manner asto permit the connection base 50 and the second arm 30 to slide on eachother. The connecting portion 51 forms a communicating portion 50 a thatallows communication between the interior of the drive motor 10 and theinterior of the second arm 30.

Specifically, with reference to FIG. 2, the industrial robot 1 has aspace (a passage) extending along a path from the fixed base 2 to themovable base 40 through the first connection shaft 5, the first arm 3,the reducer 10 b, the sleeve 17, the communicating portion 50 a, thesecond arm 30, and the second connection shaft 43. A wiring tube 60extends from the fixed base 2 to the movable base 40 along the pathdefined by the space (the passage). The proximal end of the wiring tube60 is connected to a wiring substrate or a valve (neither is shown)accommodated in an accommodation box provided in the fixed base 2.

As shown in FIG. 1, the extended portion 52 has a lower extended piece52 a and an upper extended piece 52 b. The upper end of a firstauxiliary link 55 is rotatably connected to the lower extended piece 52a. The lower end of the first auxiliary link 55 is rotatably connectedto an extended frame portion 2 a of the fixed base 2. In the illustratedembodiment, a first parallel line R1 is the line extending from thelower connection point of the first arm 3 to the lower connection pointof the first auxiliary link 55. A second parallel line R2 is the lineextending from the upper connection point of the first arm 3 to theupper connection point of the first auxiliary link 55 The first arm 3,the first auxiliary link 55, the first parallel line R1, and the secondparallel line R2 each correspond to one of the sides of a parallelogram.Further, the first arm 3, the first auxiliary link 55, the fixed base 2,and the connection base 50 form a first parallel link mechanism P1having the fixed (immobile) first parallel line R1.

The lower end of a second auxiliary link 56 is rotatably connected tothe upper extended piece 52 b. The upper end of the second auxiliarylink 56 is rotatably connected to the movable base 40. In theillustrated embodiment, a third parallel line R3 is the line extendingfrom the lower connection point of the second arm 30 to the lowerconnection point of the second auxiliary link 56. A fourth parallel lineR4 is the line extending from the upper connection point of the secondarm 30 to the upper connection point of the second auxiliary link 56.The second arm 30, the second auxiliary link 56, the third parallel lineR3, and the fourth parallel line R4 each correspond to one of the sidesof a parallelogram. Further, the second arm 30, the second auxiliarylink 56, the connection base 50, and the movable base 40 form a secondparallel link mechanism P2.

A robot arm mechanism 61 is provided on the movable base 40. The robotarm mechanism 61 has a first horizontal arm 62, a first joint shaft 63,a second joint shaft 64, and a second horizontal arm 65. The firsthorizontal arm 62 rotates about the first joint shaft 63, which isprovided at the proximal end of the first horizontal arm 62. The secondjoint shaft 64 and the second horizontal arm 65 are arranged at thedistal end of the first horizontal arm 62. The second horizontal arm 65rotates about the second joint shaft 64, which is provided at theproximal end of the second horizontal arm 65. An operation shaft 66 isrotatably supported by the distal end of the second horizontal arm 65.An end effecter such as a hand device (not shown) is secured to theoperation shaft 66.

Operation of the industrial robot 1 will hereafter be explained.

Specifically, as shown in FIG. 4, operation of the industrial robot 1when the movable base 40 moves from the position indicated by the soldlines to the position indicated by the chain double-dashed lines will bedescribed.

First, to pivot the first arm 3 and the second arm 30, the drive motorbody 10 a is actuated to rotate the input shaft 21 of the reducer 10 bin a counterclockwise direction. This causes the first output shaft 27to rotate in a clockwise direction, the opposite direction of therotational direction of the input shaft 21, through the first flexspline24 and the first gear portion 26 a of the circular spline 26. The firstoutput shaft 27 adjusts the angle θa of the first arm 3 with respect tothe horizontal line D1 through rotation.

The second output shaft 29 rotates in the clockwise direction, theopposite direction of the rotational direction of the input shaft 21,through the second flexspline 25 and the second gear portion 26 b of thecircular spline 26. The second output shaft 29 adjusts the angle θbbetween the first arm 3 and the second arm 30 through rotation.

When the first output shaft 27 rotates in the clockwise direction, thefirst parallel link mechanism P1 maintains the second parallel line R2in a state parallel with the first parallel line R1. In other words, thefirst parallel link mechanism P1 pivots the first arm 3 and the firstauxiliary link 55 while maintaining the horizontal line D1 passingthrough the connection base 50 parallel with the floor surface B. Inthis manner, the connection base 50 is moved from the position indicatedby the solid lines to the position indicated by the double-dotted brokelines as in FIG. 4.

When the first output shaft 27 rotates in the clockwise direction, thesecond output shaft 29 rotates in the clockwise direction (the samedirection as the rotational direction of the first output shaft 27) at arotational angle twice as large as that of the first output shaft 27.That is, when the angle θa increases by an amount corresponding to therotational angle θ, the second output shaft 29 increases the angle θb byan amount corresponding to a value twice as large as the rotationalangle θ and the angle θc by an amount corresponding to the rotationalangle θ. As a result, the second output shaft 29 maintains the anglesθa, θc as equal values.

When the first output shaft 27 rotates in the clockwise direction, thesecond parallel link mechanism P2 maintains the fourth parallel line R4in a state parallel with the third parallel line R3. Specifically, thesecond parallel link mechanism P2 pivots the second arm 30 and thesecond auxiliary link 56 while holding the movable base 40 in ahorizontal state. In this manner, the movable base 40 is raised from theposition indicated by the solid lines on the vertical line C1 to theposition indicted by the chain double-dashed lines on the vertical lineC1, as in FIG. 4.

Contrary, to lower the movable base 40 from the position indicated bythe chain double-dashed lines to the position indicated by the solidlined, the input shaft 21 of the reducer 10 b is rotated in theclockwise direction.

The illustrated embodiment has the following advantages.

The one-input two-output spur gear reducer 10 b, or the harmonic drivegear reducer 10 b having the single input shaft 21 and the two outputshafts 27, 29, is employed as a transmission mechanism. Therefore, byrotating the input shaft 21 through actuation of the drive motor body 10a, the first output shaft 27 (the first arm 3) and the second outputshaft 29 (the second arm 30) can be rotated. That is, pivot of the firstarm 3 and rotation of the second arm 30 can be achieved simply bysecuring the connection base 50 and the second arm 30 to the firstoutput shaft 27 and the second output shaft 29, respectively, of thereducer 10 b, which has been designed in advance. This makes itunnecessary to engage the teeth of the corresponding gears or arrangethe motor axis and the rotational axis of each arm in such a manner thatthe axes coincide with each other, when assembling the robot 1. Assemblyof the robot 1 is thus facilitated.

The fixed base 2, the first connection shaft 5, the first arm 3, thedrive motor 10, the communicating portion 50 a of the connection base50, the second arm 30, the second connection shaft 43, and the movablebase 40 are all hollow. This provides the space (the passage) extendingfrom the fixed base 2 to the movable base 40, allowing arrangement ofthe wiring tube 60 of the robot arm mechanism and wires of the drivemotor body 10 a through the interior of the arms 3, 30 and the drivemotor 10. The wiring tube 60 is thus prevented from being exposed to theexterior and interfering with the parallel link mechanisms (the firstand second parallel link mechanisms P1, P2) and the robot arm mechanism61.

The axis of the first output shaft 27 and the axis of the second outputshaft 29 are arranged on one line. Further, the first output shaft 27and the second output shaft 29 are arranged in such a manner as toaxially overlap each other. This reduces the axial dimension of thereducer 10 b. The size of the transmission mechanism thus becomessmaller compared to a case where a spur gear is used.

The connection base 50 is arranged outside the second arm 30 withrespect to the reducer 10 b (at the left-hand side as viewed in FIG. 2).Specifically, the connection base 50 is provided outside the second arm30 with respect to the reducer 10 b at a position corresponding to aside of the second arm 30 opposed to the side corresponding to the firstarm 3. This enables accurate transmission of the output from the reducer10 b to the connection base 50 and the second arm 30, widening the rangefrom which the output of the reducer 10 b (the reduction ratio) isselected.

The first arm 3, the second arm 30, and the connecting portion 51 aresealed by the first arm cover 3 a, the second arm cover 30 a, and theconnecting portion cover 51 a, respectively. Further, the connectingportion between the first arm 3 and the first connection shaft 5, theconnecting portion between the second arm 30 and the second connectionshaft 43, the space between the connection base 50 and the second arm 30are sealed by an O-ring or the seal member 57. This structure improvesseal performance of the industrial robot 1, suppressing dust release orgrease leakage from the interior of the arms 3, 30 to the exterior. Therobot 1 thus can be operated under specific circumstances such as aclean environment.

The illustrated embodiment may be modified in the following forms.

The sleeve 17 of the drive motor body 10 a may be omitted.

The first connection shaft 5, the first arm 3, the communicating portion50 a of the connection base 50, the second arm 30, and the secondconnection shaft 43 do not necessarily have to be hollow.

Instead of providing the drive motor 10 having an integral reducer 10 b,the reducer 10 b and the drive motor body 10 a may be arrangedseparately from each other. In this case, for example, the drive motorbody 10 a may be fixed to the fixed base 2.

The ratio of the reduction ratio of the first output shaft 27 to theinput shaft 21 to the reduction ratio of the second output shaft 29 tothe input shaft 21 is not particularly restricted to 2:1, but may bealtered to any other suitable values.

The first output shaft 27 and the second output shaft 29 do notnecessarily have to axially overlap each other.

In FIG. 5, unlike the embodiment of FIG. 3, the drive motor 10 issecured to the proximal end of a second arm 30, not the distal end of afirst arm 3. The distal end of the first arm 3 is connected to thesecond output shaft 29 of the reducer 10 b. The connection base 50 isconnected to the first output shaft 27. In this case, it is preferredthat the connection base 50 be arranged outside the first arm 3 withrespect to the reducer 10 b. More specifically, it is preferred that theconnection base 50 be located outside the first arm 3 with respect tothe reducer 10 b at a position corresponding to a side of the first arm3 opposed to the side corresponding to the second arm 30.

The first parallel link mechanism P1 and the second parallel linkmechanism P2 may be arranged horizontally.

Therefore, the present examples and embodiments are to be considered asillustrative and not restrictive and the invention is not to be limitedto the details given herein, but may be modified within the scope andequivalence of the appended claims.

1. A link mechanism arranged between a fixed base and a movable base,the mechanism comprising: a harmonic drive gear reducer including abody, an input shaft, a first output shaft, and a second output shaft; afirst arm connected to both of the fixed base and the body of thereducer; a second arm connected to both of the second output shaft andthe movable base; a connection base arranged such that the second arm isbetween the connection base and the reducer, the connection base isconnected to the first output shaft; a first link connected to both ofthe fixed base and the connection base; and a second link connected toboth of the connection base and the movable base.
 2. The mechanismaccording to claim 1, wherein the first output shaft and the secondoutput shaft axially overlap each other.
 3. The mechanism according toclaim 1, wherein the ratio of a reduction ratio of the first outputshaft to the input shaft to a reduction ratio of the second output shaftto the input shaft is 2:1.
 4. The mechanism according to claim 1,wherein the reducer is integral with a motor operable to drive the inputshaft.
 5. The mechanism according to claim 4, wherein the first arm andthe second arm are hollow; wherein the drive motor is hollow; whereinthe connection base has a hollow communicating portion that allowscommunication between a hollow portion of the drive motor and a hollowportion of the second arm; and wherein the first arm, the second arm,the drive motor, and the connection base define a continuous hollowpassage.
 6. A link mechanism arranged between a fixed base and a movablebase, the mechanism comprising: a harmonic drive gear reducer includinga body, an input shaft, a first output shaft, and a second output shaft;a first arm connected to the fixed base and the second output shaft; asecond arm connected to the body of the reducer and the movable base; aconnection base positioned such that the first arm is between theconnection base and the reducer, the connection base is connected to thefirst output shaft; a first link connected to the fixed base and theconnection base; and a second link connected to the connection base andthe movable base.
 7. The mechanism according to claim 6, wherein thefirst output shaft and the second output shaft axially overlap.
 8. Themechanism according to claim 6, wherein the ratio of a reduction ratioof the first output shaft to the input shaft to a reduction ratio of thesecond output shaft to the input shaft is 2:1.
 9. The mechanismaccording to claim 6, wherein the reducer is integral with a drive motorthat drives the input shaft.
 10. The mechanism according to claim 9,wherein the first arm and the second arm are hollow; wherein the drivemotor is hollow; wherein the connection base has a hollow communicatingportion that allows communication between a hollow portion of thereducer and a hollow portion of the first arm; and wherein the firstarm, the second arm, the drive motor, and the connection base define acontinuous hollow passage.
 11. An industrial robot comprising: a firstlink mechanism including a fixed base, a connection base, a first arm,and a first link, the first arm is connected to the fixed base, thefirst link is connected to the fixed base and the connection base; asecond link mechanism including the connection base, a movable base, asecond arm, and a second link, the second arm is connected to themovable base, the second link is connected to the connection base andthe movable base; and a harmonic drive gear mechanism between the firstarm and the second arm, the harmonic drive gear mechanism including abody, an input shaft, a first output shaft, and a second output shaft,the body is connected to the first arm, the input shaft is connected tothe drive motor, the first output shaft is configured to convertrotation of the input shaft and transmit the rotation to the connectionbase, the second output shaft is configured to convert rotation of theinput shaft and transmit the rotation to the second arm.
 12. Theindustrial robot according to claim 11, wherein the ratio of a reductionratio of the first output shaft to the input shaft to a reduction ratioof the second output shaft to the input shaft is 2:1.
 13. An industrialrobot comprising: a first link mechanism including a fixed base, aconnection base, a first arm, and a first link, the first arm isconnected to the fixed base, the first link is connected to the fixedbase and to the connection base; a second link mechanism including theconnection base, a movable base, a second arm, and a second link, thesecond arm is connected to the movable base, the second link isconnected to the connection base and the movable base; and a harmonicdrive gear mechanism between the first arm and the second arm, theharmonic drive gear mechanism including a body, an input shaft, a firstoutput shaft, and a second output shaft, the body is connected to thesecond arm, the input shaft is connected to a drive motor, the firstoutput shaft is configured to convert rotation of the input shaft andtransmit the rotation to the connection base, the second output shaft isconfigured to convert rotation of the input shaft and transmit therotation to the first arm.
 14. The industrial robot according to claim13, wherein the ratio of a reduction ratio of the first output shaft tothe input shaft to a reduction ratio of the second output shaft to theinput shaft is 2:1.